Corrosion protection may take a variety of forms, including utilizing corrosion-resistant metal alloys, isolating dissimilar metals, applying chemical conversion coatings, plating metals, and applying sealants (e.g., paint, epoxy, polyurethane). Sealants and other surface barriers generally protect the underlying metal from corrosion by isolating the metal from the environment. If the integrity of the surface barrier is compromised, for example, because the barrier does not adhere well to the metal or because the barrier is damaged (cracked, scratched, etc.) or degraded (e.g., weathered), the underlying metal may be exposed to corrosive conditions. Complicating the threat of corrosion due to loss of surface integrity, the underlying structures typically are exposed to stresses that may cause microscopic and/or macroscopic deformations in both the structure and the surface coating. For example, temperature fluctuations may cause expansion and contraction. Further, some structures, like the wing of an aircraft, experience large-scale flexing during ordinary use.
The corrosion protection performance (also referred to as barrier performance) of a coating, a plating, a sealant, or other barrier conventionally is assessed with an accelerated environmental exposure test such as a neutral salt spray test (also referred to as a salt fog test). In a neutral salt spray test, a test sample with a metal substrate is exposed to a spray of a standardized aqueous salt solution and then evaluated for corrosion effects. Some applications may deem corrosion protection performance acceptable when no significant corrosion occurs within 24 hours, 48 hours, 100 hours, 300 hours, 1,000 hours, or longer.
However, accelerated environmental exposure tests such as neutral salt spray tests do not simulate all the stresses experienced by corrosion protection systems. Thus, there exists a need for improved, and/or more comprehensive testing techniques.